"Patent trolling" is a real problem to tech corporations nowadays. It means that to compete with other companies, some technology companies will sell patents to licensing and intellectual property firms, legally enforcing the patents they have bought. After that, these property firms will take the targeted companies to court action for the patents. And the companies selling the patent will hide behind the property firms, they cannot be countersued as they don't stand to make money from court action.

According to the comments, the number of court cases filled today by patent trolls is 4 times more than that in 2005, and they account for almost 2/3 of all parent litigation. Also according to Google, the main victims of patent troll court action are small and medium sized companies. Last year, the toll that US companies had to take because of paten trolls was $80 billion in direct and indirect costs.

To reduce assertions and litigation from the trolls, and increase freedom while respecting legit intellectual property claims, Google has proposed multi-party royalty-free patent licensing. Recently, Google has promised not to sue open source projects using its registered intellectual property.

However, Google is also known for using the patent troll tactic against competitors. In 2011, Google gave HTC, the mobile maker from Taiwan, 5 patents to assert against Apple. But this move failed last year when a judge disallowed it. Last month, Google appealed a ruling by a US district court judge
that limited the injunctive relief available to the company if Apple
were to refuse to pay license fees to it.